METHOD DEVELOPMENT FOR PRECONCENTRATION AND QUANTIFICATION OF CRITICAL VALUABLE ELEMENTS IN PERMIAN BASIN PRODUCED WATERS

Produced waters are the most voluminous byproduct of oil and gas production. In 2017, 41% of US produced water came from Texas oil wells and is largely disposed of through subsurface injection. Due to competition for disposal space, and concerns over corresponding impacts new solutions have become necessary. Permian Basin produced waters exhibit total dissolved solids (TDS) concentrations up to and exceeding 300 g/L (dominated by Cl, Ca, and Na) and may represent a Critical and Valuable Element (CVE) source , which could be sold to defray disposal and treatment costs and provide a domestic CVE supply. This project endeavors to develop a high salinity-specific method to quantify CVEs (defined here as Au, Ag, Co, Ga, Ge, In, Nb, PGEs, REEs, Se, Te, Re) in produced waters of the Permian Basin through preconcentration and purification using Chelex-100 ion exchange resin followed by quantification via ICP-MS. Initial work focuses on testing CVE recovery from synthetic Na-Ca-Cl brines (50-300 g/L TDS) using a Chelex-100 minicolumn developed by Zhu et al. (2005), which requires much less sample (~50 mL), resin (<1 mL), and solution volumes than other methods. In this method, trace elements are preconcentrated by injecting ~50 mL of synthetic brine sample through a Chelex-100 resin minicolumn, washing with 1M ammonium acetate and water to remove the sample matrix, and eluting CVEs using 2 M nitric acid. This method, has not been tested on solutions more saline than seawater (35 g/L), solutions of variable Ca/Na ratios, or at various temperatures, which will be explored here. Na-rich (Na/Ca molar = 50) synthetic solutions up to 300 g/L carryover <100 mg/L combined of Na and Ca from the column preconcentration process suggesting that CVE recovery can be tested directly using this method without sample dilution on Na-rich solutions. However, Ca-rich (Na/Ca molar ratio = 5) synthetic solutions elute much higher concentrations of Na and Ca which may represent an analytical challenge. Results of CVE recovery via Chelex-100 minicolumn preconcentration and ICP-MS quantification at a range of pH, salinity, and temperature using the synthetic solution will be presented. Improved analytical methods to quantify CVEs in waste products, such as those being developed here, are a necessary step toward strengthening domestic CVE supplies.